Does solar work in a power outage? Why grid-tied panels shut off, and the three ways around it

Why a grid-tied inverter turns the panels off

Solar panels make direct current. The inverter converts it to the alternating current your house and the grid use, and on almost every residential system that inverter is a grid-following design. The U.S. Department of Energy describes these traditional grid-following inverters as needing an outside signal from the electrical grid to time their switching. When the grid signal disappears, the inverter has nothing to follow. That alone would stop most systems, but there is also a deliberate safety rule behind the shutdown.

The rule exists because of a condition engineers call islanding: a pocket of the distribution network that stays energized by local generation after the utility supply has gone. The Department of Energy's explainer on distributed energy resources warns that an islanded grid could damage connected equipment or injure workers who think it is disconnected from power, and it notes that many solar energy systems are programmed to detect islanding and disconnect from the grid if it occurs. Put plainly, a line crew repairing a downed wire assumes that wire is dead. A rooftop system quietly pushing power back up the line would break that assumption.

Two standards sit behind the hardware. IEEE 1547, the IEEE Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces, sets the technical requirements for connecting resources such as rooftop solar to the utility system; its published scope lists response to abnormal conditions and islanding among the subjects it covers, and the current edition was published in 2018 with a 2020 amendment. UL 1741, the safety standard for inverters, converters, controllers and interconnection system equipment used with distributed energy resources, supplements IEEE 1547 for equipment operated in parallel with the grid and points to IEEE 1547.1 for conformance testing. Your utility's interconnection rules and the inspector who signs off your permit lean on that pair. The practical result for you is simple: a listed grid-interactive inverter is designed to stop exporting when the grid is down, and you should not want it any other way.

What actually happens on your roof when the lights go out

The shutdown is quiet. Nothing on the roof moves and the panels keep receiving sunlight, but the inverter stops converting it. Here is what you will notice, and what each observation means:

• The house is dark at midday. This is the inverter doing its job, not a fault. The panels cannot serve your own circuits because the house wiring is still connected to the dead utility line.
• Monitoring may go blank. Many monitoring systems report through your home internet. With the router unpowered, the app may show no data until power returns, which says nothing about the health of the panels.
• Microinverters and other panel-level electronics do not change the outcome. Panel-level electronics are still grid-interactive equipment. Plug-in balcony kits follow the same rule: the state laws that legalize them require a feature that stops them energizing the house wiring in an outage. Moving conversion to each panel changes shade handling and monitoring, not outage behavior.
• Switching off your main breaker does not create backup. Opening the main isolates the house, but the inverter still has no grid signal to follow, so it stays off. Getting power to the house during an outage takes equipment designed to form its own electrical reference, described below.
• Restart is automatic. A grid-tied inverter is designed to reconnect on its own once it sees normal grid conditions again, usually after a short waiting period described in its manual. If yours stays off long after the grid returns, check the inverter display and your installer's instructions before resetting anything.

One more consequence matters for payback: while the system is off it earns nothing. A long outage on a sunny week costs you the production you would have used or exported. For most homes that is a small share of a year, as the outage data later on this page shows, but if your quote carries a production guarantee, check whether outage downtime counts against it. Read that clause when you check the quote against the red flags guide.

The three ways a solar home keeps power on

Every working backup arrangement solves the same two problems. It must separate the house from the utility line so nothing flows back toward the street, and it must provide an electrical reference the solar equipment can follow, or replace the solar output entirely. The three common routes do that in very different ways, with very different results.

Route 1: a battery system built to island the house

This is the route most people mean when they say solar backup. A battery inverter that is designed to operate without grid support, which the Department of Energy describes as possible only for solar-plus-battery systems designed to do so, forms its own electrical signal for the house. Isolation equipment installed with it opens the connection to the utility when the grid fails, so the house becomes its own small island and the line outside stays dead. The solar array can then keep working, because it is following the battery inverter's signal instead of the grid's.

Two design choices decide what you get. The first is coverage: a backup system either feeds a short list of circuits moved to a separate critical-loads panel, or it is installed to back up the whole main panel, in which case your own discipline during an outage decides how long the battery lasts. The second is coupling. In a DC-coupled design the panels and the battery share one hybrid inverter; in an AC-coupled design a separate battery inverter sits beside your existing solar inverter, the usual route when adding a battery to existing solar. Either can work in an outage if the system is designed and configured for it, and that last clause is the one to get in writing. A battery installed only for time-of-use shifting or export management is not automatically a backup system.

Route 2: a backup-capable inverter with no battery

Some grid-tied string inverters include a limited emergency outlet that can deliver power from the panels while the sun is shining and the grid is down, with the inverter disconnected from the utility. It is not whole-house backup and it is not something to assume. The output is small, it varies with every cloud, and it stops at sunset. For charging phones, running a small refrigerator by extension cord for part of the day, or keeping a router alive, it can be useful at little or no extra cost.

We could not find a government or standards-body source that describes this feature category in general terms, so treat it strictly as a datasheet item: ask whether the exact inverter model on your quote has a sunlight-only outlet, what its rated output is, and where it will be mounted. If the answer is vague, assume the feature is absent.

Route 3: a generator wired through a transfer switch or interlock

A fuel generator does not care whether the sun is up. Connected to the house through a transfer switch or a panel interlock, it powers selected circuits while the house is mechanically separated from the utility line. That separation is the same worker-safety principle that makes the solar inverter shut down: the street side must stay dead. A generator backfed into a dryer outlet with a homemade cord skips the separation and puts line crews, and you, at risk; the connection hardware is electrician work with a permit.

On a solar home, the generator usually runs the house while the solar system stays off, because a grid-tied inverter will not treat a generator as the grid unless the whole system was designed for it. Pairing a generator with a solar-plus-battery system to recharge the battery is possible, but it is a design question for the battery's specification, not a default. Federal emergency guidance on Ready.gov is blunt about placement: generators and fuel should always be used outdoors and at least 20 feet away from windows, doors and attached garages, with working carbon monoxide detectors on every level of the home. EnergyBS prices the connection hardware in its transfer switch and interlock cost guide and permanent units in its standby generator cost guide, so this page does not repeat those prices.

How long outages actually last, by the federal numbers

Backup should be sized to the outages you are likely to get, not to the worst storm in an advertisement. The U.S. Energy Information Administration publishes reliability data from utility reports, and its January 25, 2024 analysis of 2022 data found that U.S. electricity customers averaged about five and one-half hours of power interruptions that year, counting major events, across roughly 1.4 interruptions per customer. Excluding major events such as severe weather and vegetation contact, the average duration has stayed consistently around two hours a year since 2013, according to the same analysis.

Averages hide the places where backup earns its keep. In 2022, EIA reported that customers in Florida, West Virginia, Maine, Vermont and New Hampshire had the longest interruptions, ranging from an average of 10.3 hours in New Hampshire to 19.1 hours in Florida. At the other end, customers in the District of Columbia, Delaware, Rhode Island, Nebraska and Iowa averaged between 34 and 85 minutes. Those are yearly totals per average customer, not single events, but they show why the same battery can be a luxury in one state and a sensible purchase in another.

Two cautions. EIA's figures are customer averages: if you live at the end of a long rural line, your history may look nothing like your state's. And a single hurricane or ice storm can produce a multi-day outage that no yearly average describes. If a multi-day event is the scenario you are buying for, size the recharge side of the system, covered below, as carefully as the battery.

Sizing backup to the outage, not to the brochure

A battery has two ratings that matter in an outage. Power, in kilowatts, is how much it can deliver at one moment, and it decides whether the battery can start and run a given load at all. Energy, in kilowatt-hours, is how much it holds, and it decides how long the house runs. The Department of Energy makes the same point in its solar-plus-storage explainer: a storage system is described by both its capacity and its storage time, so you can get a lot of power for a short time or less power for longer. NREL's 2024 Annual Technology Baseline uses a 5 kW, 12.5 kWh system as its representative residential battery, which is 2.5 hours at full output.

Runtime is arithmetic once you know your loads: the energy you allow the battery to deliver, divided by the average power the house draws. Two inputs come from you. The first is the usable capacity from the battery's datasheet, minus any reserve you want to keep for the next night. The second is the average draw of the circuits you will back up, which a critical-loads list makes concrete. EnergyBS has a full critical-load sizing and runtime guide with device-by-device loads, so this page stays on the solar side of the decision: how the array refills the battery, and what the quote should say.

1. List the circuits you cannot do without for 24 hours. Refrigeration, a few lights, internet, a furnace blower or a sump pump are typical. Mark anything with a motor, because motors draw a surge when they start.
2. Ask the installer for the battery's continuous and peak power ratings and check every motor load on your list against them. A load that will not start is not backed up, however many kilowatt-hours sit in the battery.
3. Estimate the average draw of the list in watts, then divide the usable kilowatt-hours you plan to use by that average in kilowatts. That is your no-sun runtime.
4. Compare the runtime with the outage profile above. If one night covers your realistic outage, you are done. If you need more, decide between a larger battery, a shorter list, and recharge from the array, which is usually the cheapest of the three.

Can the panels refill the battery during a long outage?

Yes, if the system is designed for it, and this is the feature that turns a one-night battery into multi-day backup. Once the battery inverter has islanded the house, it provides the electrical reference the solar inverter needs, and daytime production can serve the house and recharge the battery. Whether your system does this depends on how the array and battery are coupled and configured, so ask the question directly and get the answer on the design documents rather than in a sales conversation.

Scale matters. As a planning illustration, an 8 kW array in a climate producing 1,400 kWh per kW per year, the planning factor used in this site's sizing guide, makes 8 times 1,400, or 11,200 kWh a year, which averages about 30.7 kWh a day. That is an annual average. A short winter day or a storm-covered sky can deliver a fraction of it; for a house with no utility line at all, those days set the size and price of the whole system, worked through day by day in what an off-grid solar system costs at the DOE benchmark. Even so, a third of the average day is about 10.2 kWh, which is roughly a night of critical loads in the worked example below.

Two limits cut in. First, when the battery is full and the house is drawing little, the surplus has nowhere to go, because exporting to the dead grid is exactly what the system must not do, so production has to be throttled back. Second, during the day the battery's power rating still caps what the house can run at one moment, even if the panels are producing more. Neither limit is a defect; both are reasons to size the critical-loads list honestly.

What backup costs on a solar quote now

The cleanest public anchor is the U.S. Department of Energy's Q1 2025 photovoltaic system cost benchmarks, produced with the national laboratory formerly called NREL. For an 8 kW residential rooftop system, the modeled market price is $2.95 per watt DC for solar alone and $4.59 per watt DC for solar plus a 13.5 kWh battery, in 2024 dollars. Multiplied out, that is $23,600 without storage and $36,720 with it, a gap of $13,120, or about $972 per kilowatt-hour of battery nameplate once the battery's share of installation and integration is folded in. This is a modeled benchmark, not a market survey and not a quote, but it gives you a scale for the battery line on your own paper. The same $2.95 per watt solar-only figure is the comparison line this site uses in the cost guide and in the estimator, so the solar part of a battery quote can be read against the same line as a solar-only quote.

There is no federal discount to subtract. The IRS Residential Clean Energy Credit page, last reviewed July 4, 2026, lists battery storage of at least 3 kWh as qualifying property beginning in 2023, and also states that the credit is not available for any property placed in service after December 31, 2025. A battery installed in 2026 therefore starts from its full price. If a 2026 quote shows a backup system net of a 30 percent federal credit, the number is stale; the credit status page explains what ended and why the installation date decides it. State and utility storage programs still exist in some places and are tracked in DSIRE; check them through the incentives checklist rather than trusting a printed figure.

Price the backup on its own line, and read what a utility battery program may take from that backup before you enroll. A combined quote hides both the solar price per watt and the battery premium, and you cannot judge either. Also look for the electrical work that backup can trigger: moving circuits to a critical-loads panel, isolation equipment, and sometimes work on the main panel itself. Whether a panel upgrade line is genuine is a busbar arithmetic question covered in the main panel upgrade guide. For market battery prices and installation bands, EnergyBS keeps a home battery installation cost guide, and its battery value analysis covers the bill-savings side.

Paperwork: permits, interconnection and your export rule

A backup battery is a change to your interconnected system, not just an appliance. Expect an electrical permit and an inspection, and check whether your utility requires an updated interconnection application before the modified system operates, since the equipment connected to its network has changed. If you are adding storage to a system that already has permission to operate, ask the installer to confirm in writing who files with the utility, what the utility's review timeline is, and whether the system may run before approval. The installation process guide walks the same permit and approval stages for a new system.

The battery can also change how your exports are billed. Ask your utility, before you sign, whether adding storage affects the tariff your existing solar sits on, and whether the answer depends on how the battery is configured to charge and discharge. Read your current tariff, or the export compensation explainer, before you sign, and if you are in California, the Net Billing Tariff guide covers how storage interacts with export values there. Where exports are paid well below retail, a battery bought for backup may also earn bill savings, which can change the economics in its favor; where exports earn near retail, backup is mostly what you are paying for.

A decision path for the solar owner

Put the pieces together in order. The table runs from the cheapest question to the most expensive answer, so stop at the first row that settles your situation.